Vehicle occupant position detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and/or how forcefully, to deploy the restraint. Ideally, the system should be capable of classifying the type of occupant (i.e., large adult, small adult, child, etc.) and the position of the occupant relative to the point of deployment of the air bag. Various systems incorporating one or more infrared and/or acoustical ranging sensors have been proposed for this purpose; see, for example, the U.S. Pat. Nos. 5,330,226 and 5,785,347. In general, such systems emit one or more beams of infrared energy to define a corresponding number of viewing fields, and receive the reflected energy to detect the presence of an occupant within the viewing fields. However, the information obtained by such techniques is sometimes corrupted by other light sources (such as reflected sunlight, or pulsed incandescent light), and even under best conditions is typically insufficient to accurately classify the occupant type and position. For example, it may be desired to deploy an air bag even though the occupant's hand or arm is near the point of deployment, but undesirable to deploy if the occupant's head or torso is near the point of deployment. For this reason, other position sensors or weight sensors are typically used in combination with a ranging sensor to provide a more comprehensive understanding of occupant classification and position. Unfortunately, such systems tend to be quite costly, and are difficult to package in the automotive environment. Moreover, a relatively high speed of response is required so that deployment can be properly inhibited or allowed when the occupant position quickly changes, possibly in anticipation of an impending collision. Accordingly, what is needed is a low-cost system that can accurately and quickly recognize an occupant for purposes of classification and position.